Ticket #50696: 50696.patch

src/wp-admin/css/customize-controls.css

@@ -1075 +1075 @@
 #available-menu-items .new-content-item .create-item-input,
 .customize-control-dropdown-pages .new-content-item .create-item-input {
         flex-grow: 10;
+        width: 100%;
 }
 
 #available-menu-items .new-content-item .add-content,

src/wp-admin/css/customize-nav-menus.css

@@ -606 +606 @@
 #available-menu-items .new-content-item .create-item-input.invalid,
 #available-menu-items .new-content-item .create-item-input.invalid:focus {
         border: 1px solid #dc3232;
+        box-shadow: 0 0 2px rgba(204,0,0,.8);
 }
 
 #available-menu-items .menu-item-handle .item-type {